CONSTRUCTION OF A CUT-OFF WALL FOR EXISTING TAILINGS IN WARM PERMAFROST IN ALASKA

Franz-Werner Gerressen¹

¹ BAUER Maschinen GmbH

Baixar PDF doi:10.20906/CPS/CB-03-0006

Resumo

Diaphragm walls are mainly known as underground structural elements commonly used for retention systems and permanent foundation walls or elements. Of course they can also be used as deep groundwater barriers, which this paper is going to show. Therefore the paper will describe the construction method and the sequence of activities required for the construction of cut-off-walls using a trench cutter system. It will describe also the main equipment which will be needed to execute these works. In particular the focus will be taken to a cut-off wall which has been designed along the Back Dam of the existing tailings impoundment at Red Dog Mine, Alaska. The cut-off wall was about 1525 m long and up to 45 m deep. The tailings impoundment is situated in an area of warm permafrost and high potential seismic activity. Design incorporated an assessment of rock jointing to define the final depth of the wall along the alignment requiring the use of plastic concrete backfill to address the concerns associated with potential cracking of the wall due to settlement and during seismic activity. The cut-off wall has being constructed by GAIAContractors, the wholly owned specialized contracting subsidiary of Golder's Canadian company. About 371 m² of cut-off wall was constructed in 2007 to evaluate the performance of the cutter heads, the slurry transport systems, and the mix design. Cut-off wall construction continued in 2008 and 2009 operating with two 12-hour shifts from May to October. Approximately 13,750 m² of wall was completed in 2008 and 13,935 m² in 2009. The trench cutter method is an ideal tool for both the construction of diaphragm walls and for the construction of deep cut-off walls. Experience on the Red Dog project indicates that the trench cutter is very effective in the construction of deep cut-off walls extending through both overburden and rock and that it is worthy of consideration particularly for projects where grouting of weathered and/or fractured rock may be considered the only alternative. Care

Palavras-chave: Cut Off Wall; Tailings; Cutter